This experimental core component of the Center has four goals: (1) a study of the maturation of brain morphology in normal children, as reflected in magnetic resonance imaging (MRI), from birth to eight years of age; (2) an effort to define deviations from normal maturation in children with focal damage to the cerebrum sustained early in life; (3) an examination of brain morphology in infants and children with two forms of severe mental retardation; (4) maintenance of an archive of clinical brain-imaging studies (films and, when available, tapes) obtained for other children participating in the Center studies. The results of our recent studies underscore the importance of learning more about the nature of normal brain maturation in younger children, and of defining any alterations in these normal processes that attend early damage to the brain. We, therefore, propose a major focus on the study of normal children aged 0 to 8 years, and children with single focal lesions in the distribution of the middle cerebral artery due to vascular damage sustained during the first year of life. The primary goals of this comparative study will be: (1) to define the nature, location, and extent of acute vascular lesions in a group of babies with focal brain damage; (2) to characterize the residual and secondary effects of these lesions on brain morphology in two year olds; (3) by comparison of these images to those from normal age-matched controls, to determine if and how the lesions affect the maturation of the brain; and (4) to relate the effects on brain morphology to the acute and long-term behavioral consequences of the lesions. A second study will follow-up on earlier studies of WS and DS will compare infants with WS and 8-year-old children with both syndromes to age-matched controls. These studies will be both cross-sectional and longitudinal in nature. Their designs reflect to a considerable degree the ethical constraints relevant to the study of young children. The aim of the studies with WS and DS subjects is to determine (1) to what extent the gross morphological abnormalities observed in older WS and DS children are fully present soon after birth; and (2) to what extent they evolve through interaction with post-natal maturational processes.